Traditionally, for instance, when each hollow member such as a pipe member is fastened by such as a screw, each separated outer wall of the hollow members overlapped with a different outer size is fastened as disclosed in Japanese Laid Open Patent Publication H5-146316.
Or when the outer sizes of each hollow member are the same, an inner member which is inserted into one of the hollow members from another hollow member is projected, and the outer wall of one of the hollow members and the inner member of the other hollow member are joined at an inserted position.
However, when each separated wall is fastened as disclosed in the former instance, it is different from the case when each coherent wall is fastened, and it cannot be fastened over strength in the direction of wall thickness because the fastening force acts to cave the wall in the thickness direction. Therefore when the thickness of the wall is thin, secured firming of each member may be difficult because sufficient fastening force cannot be obtained. Further there may be more or less a backlash in the joining status due to a difference between the screw hole and the screw and a process deviation of the screw hole.
On the other hand, in the latter instance, in addition to the same defect as more or less backlash in the joining status, according to this status, a defect may take place that a favorable joining status in which each end face of hollow member is joined face to face cannot be obtained (specifically there is an unexpected gap between the joining portion of each end face).